What is the difference between hydraulic oil and hydraulic fluid?

Hydraulic Oil And Fluid

Hydraulic oil or Hydraulic fluid are the two terms that most people use interchangeably. However, they are different. So, what is the difference between hydraulic oil and hydraulic fluid?

Though both are fluids, hydraulic fluid may contain other fluids such as water oil, plain water, salt solution, and water-oil emulsions. 

Hydraulic oil is flammable. You cannot use it close to an ignition source. The oil spray of hydraulic oil can ignite when subjected to high pressure. The high flammability of the hydraulic oil is the reason for developing hydraulic fluid as a solution to address the challenge.

There is much online and book content trying to explain hydraulic oil, hydraulic lubricants, and oils. If you are confused by choosing appropriate hydraulic oil for your machine, read through this article to the end and discover all you need to understand about hydraulic oil or hydraulic fluid. 

advantages of Hydrauli Oil
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What is hydraulic oil?

Hydraulic oil is a no-compressible liquid that transfers power with hydraulic machinery and equipment. Apart from moving energy, hydraulic oil also acts as a coolant, lubricant, and sealant within the equipment or hydraulic machinery.

The hydraulic oil can be either mineral-based or synthetic. Unlike mineral-based hydraulic oil, which is a derivative of the fractional distillation process of crude oil, synthetic oil is synthesized from chemical-based fluids. Synthetic oil is also enriched with other components to improve its physical attributes, such as biodegradability, oxidation, stability, and high-temperature performance.

There are three common forms of oil on the market;

Flame radiant hydraulic oil is a type of oil that is significant in machinery but has a high fire risk.

Wear-resistant hydraulic oil: This type of oil is more useful in hydraulic machinery that works under conditions of high temperature and pressure.

General hydraulic oil: General hydraulic oil is helpful in general machines because of its oxidation stability and antifriction properties.

What is a hydraulic fluid? 

Hydraulic fluid resembles hydraulic oil but differs slightly in terms of its content and applications. As explained, hydraulic fluid may contain other additives such as water, salts, and emulsions. Hydraulic fluid fluids have a broader application in the automobile systems, such as power steering, power brakes, and automatic transmissions. In addition, hydraulic fluids have several applications in aircraft systems.

hydraulic fluid
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Why hydraulic fluid is different from other hydraulic fluids 

Hydraulic oil is quite different from other hydraulic fluids. Apart from the transmission, it is also functioning as a lubricant. Therefore, it poses a dual role that makes it unique. 

In addition, hydraulic oil has some distinct properties such as air release and foaming resistance, oxidation and hydrolytic stability, anti-wear performance, ability to filter, rust, and corrosion resistance which sets it apart from other fluids.


Hydraulic fluids have significant applications in transferring energy in hydraulic systems such as excavators, hydraulic brakes, garbage trucks, and backhoes. Hydraulic oil, on the other side, is a flammable fluid that is applicable in hydraulic machinery. Hydraulic oil has physical properties that allow it to perform as a coolant, power transmitter, and lubricant. You can use Hydraulic fluid in automobile systems, automatic transmission, power steering, and power brakes.

hydraulic fluids
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As opposed to hydraulic oil, Hydraulic fluids are either less flammable or nonflammable. Therefore, they can’t be applicable in high pressure and temperature without bursting into flame.

Operation conditions 

Hydraulic fluids can perform under a wide range of temperatures and pressure. However, hydraulic oil cannot withstand high pressure and temperature. Hydraulic oil can easily burst into flame when subjected to high temperature or pressure.

You can view hydraulic oil as a form of hydraulic fluid. Both serve the purpose of transmitting power in a hydraulic system. The primary factor that makes hydraulic fluid differ from hydraulic oil Is its nonflammable property. It is also applicable in automobile systems for automatic transmission, which is a role that hydraulic oil cannot perform.

Buyer guide for hydraulic fluids and hydraulic oil 

Now that you understand the differences between hydraulic oil and hydraulic fluid, you may be asking yourself how to buy the best product for your machine. Your rule of thumb for purchasing a product is to follow the manufacturer’s recommendation.

Your machine has a recommendation for the best type of fluid to use. Before you buy, get to understand the specification of your machine specifications. Use an appropriate type of either hydraulic fluid or hydraulic oil where applicable.

The following are the primary factors to consider before buying hydraulic oil or fluid.


The viscosity of the hydraulic fluid /oil is an important aspect that determines what to buy. Density determines the adequacy of the performance of your machine. For instance, a more viscous hydraulic fluid will take more time to flow inside hydraulic machinery, lowering its efficiency and performance. On the other hand, less dense fluid is difficult to control and may vaporize. It is, therefore, essential that you chose the correct viscosity for your machine.

Hydraulics oil and Fluid
Image Source: Oil-Store.co.uk

The climatic condition of your place 

The climatic condition of your place plays a crucial role in deciding the type of hydraulic fluid or oil you need for your machine. For example, you will need to buy a more viscous fluid when you live in hot areas most of the year. This is because high temperatures reduce the viscosity of your liquid.

If you operate in cold areas most of the year, less viscous hydraulic fluid or oil will perfume well with your machine. Conversely, more viscous fluid will increase viscosity or even freeze in the cold. Therefore, you must check on the weather condition you are operating in before selecting the best product for your machine.

The natural and synthetic type 

There are two basic types of fluids that you can choose from. You can either buy natural hydraulic oil or synthetic type. 

Natural hydraulic oil type comes from crude oil. It is a cheaper and convenient option for your machine. 

Synthetic hydraulic fluid is a laboratory process that uses various chemicals. The synthetic type may be more effective in lubrication compared to the natural variety.

If you are looking for a cheaper option, natural hydraulic oil is your best option. However, when the price is not an issue, and you would like a more effective product for your machine, consider synthetic type.

Image Source: DEKRA


Hydraulic fluids are not as flammable as hydraulic oil. Avoid using hydraulic oil in places that are close to hot engines. Hydraulic fluids are the best option in areas where hydraulic fluid can trigger an easy burst into flame.


There is a significant difference between hydraulic fluid and hydraulic oil in terms of their property and functions. Hydraulic fluids are resistant to pressure and high temperatures. Its role includes the effective transmission of power, lubrication, resisting corrosion, removal of impurities, thermal oxidation, and hydraulic stabilization and prevention of wear machines. When choosing the best hydraulic fluid or hydraulic oil for your system, you must check your place’s viscosity, flammability, and climatic condition. Though synthetic and natural options may be at your disposal, analyze the costs and benefits before deciding on the type to choose. If you need top performance, consider synthetic type. However, if cost is your concern, buy natural hydraulic fluid, which is relatively cheaper.

The rule of thumb is to consider what is best for your machine. Then, consult an expert and get the recommendation that will ensure the top performance of your devices.

Feature Image Source: Backyard Boss

Mia A Chloe
Author: Mia A Chloe

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